Transformer rectifier units (TRUs) and auto-transformer units (ATRUs) are electrical power transformer units that may be used on airplanes to convert 115 volts alternating current (VAC) at 400 Hertz to 28 volts direct current (VDC) airplane power for powering electrical systems and components on an airplane. The 115 VAC may be generated by one or more electrical power generator devices that are mechanically, operatively coupled to an airplane's engine by a drive shaft and gear arrangement to convert mechanical energy to electrical energy. The largest, heaviest and highest thermal emitting component in each TRU/ATRU is the transformer core. The weight of the TRUs/ATRUs and their thermal emissions can effect performance of the airplane. The weight of the TRUs/ATRUs is subtracted from the payload weight of the airplane and therefore reduces the amount of weight that the airplane may be designed to carry. Additionally, the cooling requirements may effect engine compartment design and thermal management.